Rock drill bit



Sept. 22, 1953 J. c. CURTIS ROCK DRILL BIT Filed Mar 0h 24. 1948 John C Curfis.

Patented Sept. 22, 1953 noon DRILL Brr .l olin, Curtis, Claremont, N. H., assignor to Joy Manufacturing Company, Pittsburgh, Pa a corporation of Pennsylvania Application March 24, 1948, Serial No. 16,744

I 6 Claims. 1

This invention relates to rock drill bits having hard metal cutting edges and more particularly to. an impact type rock drill bit having the hard metal cutting edges provided by tungsten carbide inserts set into the cutting face of the bit in a novel manner.

In rock drill bits used with hammer rock drills, the rate and depth of penetration in rock formations and the overall cost of drilling are, to a large extent, determined by the durability of the cutting edges of the bit. As the cutting edges become rapidly worn, frequent resharpcning is necessary. and the hole gauge rapidly decreases so that, in, order to obtain a hole of a desired diameter, at a substantial depth, it is necessary to start with a bit of greater size and drill out a considerable excess of rock. It has been found that by using hard metal inserts to provide cutting edges, preferably inserts-composed of tunge sten carbide, the rate of drilling is quite substan ll tially increased, and the need for frequent bit changes and larger size bits to compensate for loss in gauge is much reduced if not eliminated, and the overall cost of drilling is substantially lessened. In known types of rock drill bits having tungsten carbide inserts roviding the cutting edges, considerable difficulty has been encountered in properly securing the tungsten carbide inserts in place on the bit face; and the inserts not only become quickly released but are also soon broken as the result of direct contact of the inserts at theirinner ends due to inward displacement of the inserts toward the center of the bit. The present invention contemplates improvements overrock drill bits of known types in that theb-it is constructed in a novel manner so that the tungsten carbide inserts are firmly held in position on the bit face.

An object of the present invention is to provide an improved rock drill bit. Another object is to provide an improved rock drill bit having hard metal inserts set in the bit face in a novel manner, to provide the cutting edges of the bit. A further object is to provide an improved rock drill bit having hard metal inserts set in the bit face to provide the cutting, edges and held against inward displacement toward the center of the bit by the central portion of the bit body surrounding the central cleansing fluid passage of the bit. A still further object is to provide an improved rock drill bit having a central cleansing fluid passage surrounded by the central portion of the bit body and having radial slots cut in the bit face for receiving the hard metal inserts, with the central portion of the bit body providing abutment means to prevent inward displacement of the inserts the slots toward the bit center. Yet another object is to provide an improved rock drill bit of the generally cruciform shaped, winged type commonly known as a cross bit and having radial slots cut in the faces of the wings to provide recesses for receiving hard metal inserts which provide the cutting edges of the bit. These and other objects and advantages of the invention will, however, hereinafter more fully appear.

In the accompanying drawing there are shown for purposes of illustration one form and a modification which the invention may assume in practice.

In this drawing:

Fig. 1 is a front end view of a. forged blank from which a rock drill bit is to be formed in accordance with the practice of the invention.

Fig. 2 is a view in longitudinal section through the forged blank shown in Fig. 1, illustrating certain steps in, the formation of the drill bit.

Fig. 3 is a front end view and Fig. 4 is a side elevational view of the bit blank shown in Fig. 2

.after completion of certain preliminary operations including shank threading.

Fig. 5 is a view partially in longitudinal section and partially in side elevation, illustrating another step in the formation of the drill bit.

Fig. 6 is a front end view and Fig. 7 is a side elevational view of the bit blank after the operation indicated in Fig. 5 is completed.

Fig. 3 is a view partially in longitudinal section and partially in side elevation, showing still an other step in the formation of, the bit.

Fig. 9 is an enlarged detail sectional view taken on line 9&9 of Fig. 8, showing still another step in the formation of the bit.

Fig. 10 is an enlarged perspective view of one of the tungsten carbide inserts.

Fig. 11 is a perspective view of the completed drill bit.

Fig. 12 is a front end elevational view of a completed drill bit, but illustrating a modified construction.

In accordance with the present invention a rock drill bit with hard metal inserts providing the cutting edges of the bit, is provided, and as illustrated in Figs. 1 to 9 inclusive, comprises a metal blank, generally designated !3 in Fig. 1, which is first preformed as by forging, and this blank has a forward portion of generally cruciform shape providing radial wings M. The forward face of the blank is centrally depressed at [5 during forging to provide a plane front surface It of generally circular outline, and the forged blank has a reduced rearward projection ll. Formed between the wings during forging are spaces or recesses l8 which extend rearwardly from the bit face. The forged blank, in its completed form as shown in Fig. 1, is first placed in a chuck, diagrammatically indicated at i9, of a conventional automatic rotary machine, such as an automatic lathe, and as the blank is rapidly rotated, the front surfaces of the wings are faced at 2!) and the sides of the blank are tapered at 2! by a suitable machine tool diagrammatically illustrated at 22. Figs. 3 and 4 show the bit blank after the machining operations of Fig. 2 are completed, with plane surfaces 23 on the front faces of the wings and with the sides of the bit tapered rearwardly from the front of the blank preferably at a 3 angle. The reduced projection ll of the bit blank is then threaded at 2:3, desirably by a conventional hot rolling operation and the blank is axially drilled to provide a cleansing fluid passage 25 which centrally traverses the front plane surface 16 of the central depression i5, and these steps of hot rolling the threads and axially drilling the cleansing fluid passage do not per se enter into the present invention, as they are relatively conventional. The bit blank is then placed in the head, diagrammatically illustrated at 26 in Fig. 5, of a milling machine, and radial slots 21 are cut in the faces of each wing by a conventional end milling cutter, diagrammatically illustraated at 2 Figs. 6 and 7 show the bit blank after the completion of the milling operations performed in Fig. 5. The radial slots 21 are cut deeply into the faces of the wings, with their plane bottom surfaces 29 lying in a transverse plane to which the bit axis is perpendicular and spaced rearwardly of but in parallelism with a transverse plane in which the plane surface [6 lies. The slots have parallel plane sides 30 which are joined with plane bottom surfaces 29 by curved surfaces 35. The inner end walls of the slots are of semi-cylindrical form, as indicated at 32 in Fig. 6, and these end walls are joined with the plane bottom surfaces 29 of the slots by curved surfaces 33, shown in Fig. 8. Thus, all sharp corners which might result in breakage upon application of working pressures to the bit are avoided. Subsequent to the slotting operation,

preformed hard metal inserts 34, preferably composed of tungsten carbide, are secured, as by suitable brazing material or silver solder indicated at 35 in Fig. 9, within the slots, with the sides, ends and bottom surfaces of the inserts firmly secured to the surfaces 29, 39 and 32 of the slots. The junctions of the side and bottom surfaces, of the bottom and inner surfaces and of the inner and side surfaces are preferably all smoothly rounded. The spaces left between the upper edges of the slot side-walls 30 and the upper side edges of the inserts are filled with brazing material, as at 39 in Fig. 9, to supplement the brazing at the sides, bottoms and ends of the inserts in the firm securing of the inserts in position. The outer edges of the wings and inserts are then beveled at 40 as by grinding, as shown in Fig. 11, to remove any sharp outer edges which might result in breakage of the inserts during operation of the bit if not removed. The central portion 41 of the bit body is generally annular, as shown in Figs. 6 and 8, and the inner walls 32 of the radial slots may cut slightly into this central annulus, as shown in Fig. 6. This generally annular central portion supports the inner walls 32 of the slots and provides an abutment to prevent inward displacement of the inserts in the slots toward the bit center. When the inserts are secured in position in the slots, the upper portion 42 thereof extend forwardly from the sides of the slots 21 and have relatively inclined upper surfaces 43 which terminate in cutting edges 44, with the cutting edges located in advance of the forward faces of the wings. The completed rock drill bit is shown in Fig. 11, and the recesses or spaces [8 between the bit wings provide adequate flow area for the cleansing fluid as it flows from the passage 25 across the bit face between the inserts and rearwardly from the drill hole.

In the modification shown in Fig. 12, the drill bit is made in the same manner as the form above described but the central passage for the cleansing fluid is omitted and a passage 45 for cleansing fluid opens through the side of the bit face between a pair of the inserts, and the hole 45 is inclined rearwardly and inwardly to join with an axial passage 4% formed in the projection H, as shown in dotted lines in Fig. 12. With this modified cleansing fiuid passage arrangement, the plane surface 16 at the bottom of the depressed portion l5 at the center of the bit face is imperforate. If desired, additional outwardly inclined passages 45 may be arranged between the other wing-pairs in an obvious manner.

As a result of this invention, an improved rock drill bit is provided having hard metal inserts firmly set in the bit face in a novel manner, to provide wear resisting cutting edges of the bit. By the provision of the radial slots cut in the front faces of the bit wings and terminating at points spaced from the center of the bit, the central portion of the bit body between the slots provides an abutment for the inner ends of the hard metal inserts received in the slots, thereby preventing inward displacement of the inserts inv the slots toward the bit center. By the novel steps of manufacture disclosed, an improved drill bit is provided, resulting in the firm securing of the tungsten carbide inserts in the bit face in an improved manner. Thus, an improved rock drill bit with hard metal, wear resisting cutting edges is provided whereby the rate of drilling is quite substantially increased and the overall cost of drilling is substantially lessened. These and other advantages of the invention will be clearly apparent to those skilled in the art.

While there are in this application specifically described one form and a modification thereof which the invention may assume in practice, it will be understood that this form and modification of the same are shown for purposes of illustration and that the invention may be further modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. A percussive rock drill bit comprising a bit body having a generally cruciform shaped forward portion providing cross wings and a depressed central body portion traversed by a cen tral cleansing fluid passage, slots formed in the front faces of said wings and extending radially with respect to the bit center and terminating at their inner ends at points spaced equidistantly from the central portion of the bit body surround-ing said cleansing fluid passage, and tungsten carbide inserts bonded in said slots with their forward portions projecting forwardly from said central portion and providing cutting edges, said central body portion surrounding said cleansing fluid passage, supporting the end walls of said slots and providing an abutment positively to prevent inward endwise displacement of said inserts in said slots toward the bit center.

2. A percussive rock drill bit comprising a bit body having a generally cruciform shaped forward portion providing cross wings and a central body portion traversed by a central cleansing fluid hole and having a forward setback portion surrounding the cleansing fluid passage and traversed by the latter, slots formed in the front faces of said wings and extending radially of the bit center and terminating at their inner ends near the periphery of said set-back portion at points spaced equidistantly from the bit-center, tungsten carbide inserts secured by bonding in said slots with their forward portions projecting forwardly in advance of said central set-back portion and providing cutting edges, said central body portion surrounding said cleansing fluid passage, supporting the end walls of said slots, and providing a central abutment positively to prevent inward endwise displacement of said inserts in said slots toward the bit center, and the cutting edges of said inserts being disposed in advance of the forward surface of said set-back portion.

3. A percussive type cross bit for drilling rock comprising a winged body of generally cruciform shape at its forward portion, and a central cleansing fluid passage, radial slots formed in the Wing faces and having semi-cylindrical inner end walls spaced equidistantly from the central portion of the bit body surrounding said cleansing fluid passage, said central portion of the bit body supporting said inner end walls of said slots, and tungsten carbide inserts bonded in said slots with their forward portions projecting forwardly in advance of said central body portion and having semi-cylindrical inner end surfaces abutting said inner end slot walls, said end abutting surfaces positively preventing inward endwise displacement of said inserts in said slots toward the bit center.

4. A percussive rock drill bit having a body formed with a forward portion of generally cruciform shape providing wings, radial recesses formed in said wings each having parallel plane side surfaces and a plane bottom surface joined with said side surfaces by curved surfaces and having a curved end wall, said curved end walls spaced equidistantly from the center of the bit by the central portion of the bit body and joined with said plane bottom surface by curved surfaces, and tungsten carbide inserts bonded in said recesses with their forward portions projecting forwardly in advance of said central body portion to provide radial cutting edges and having side, bottom and end surfaces fitting and secured by bonding material to said recess surfaces, the central portion of said bit body supporting said curved end surfaces of said recesses and providing an abutment positively to prevent inward endwise displacement of said inserts in said recesses toward the bit center.

5. A rock drill bit of the rotatable, impact type comprising a body having a forward portion and radial slots formed in said forward portion radially of the bit with the curved inner ends of said slots spaced equidistantly from the bit center, with the central portion of the body supporting the inner curved Walls of said slots, said bit having preformed inserts of tungsten carbide bonded in said slots, with the sides, bottom and curved inner ends of said inserts bonded to the slot walls and bottoms, said inserts providing cutting edges, and said central portion of said body providing an abutment for said inserts for positively preventing inward endwise displacement of said inserts in said slots toward the center of said bit.

6. A rock drill bit of the rotatable, impact type comprising a body having a forward portion and radial slots formed in said forward portion radially of the bit with the curved inner ends of said slots spaced equidistantly from the bit center, with the central portion of the body supporting the inner curved walls of said slots, said bit having preformed inserts of tungsten carbide bonded in said slots, with the sides, bottom and curved inner ends of said inserts bonded to the slot walls and bottoms, and said central portion of said body providing an abutment for said inserts for positively preventing inward endwise displacement of said inserts in said slots toward the center of said bit, said slots having their side walls of slightly greater height than the height of said inserts so that said walls project outwardly a slight distance in advance of the sides of said inserts, and the spaces thus provided being filled with bonding material so that a smooth outer surface joins the insert faces with the front face of said body.

JOHN C. CURTIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,929,608 Rea Oct. 10, 1933 2,022,194 Galvin Nov. 26, 1935 2,101,376 Voigtlander Dec. 7, 1937 2,136,083 Nast Nov. 8, 1938 2,159,842 Cook May 23, 1939 2,252,745 Williams Aug. 19, 1941 2,502,128 Curtis Mar. 28, 1950 FOREIGN PATENTS Number Country Date 25,805 Australia Dec. 23, 1935 70,945 Norway Sept, 2, 1946 530,113 Great Britain Dec. 5, 1940 OTHER REFERENCES Ser. No. 384,737, Meutsch (A. P. C.), published May 25, 1943, abandoned. 

